We aim to validate a technique of endothelial functional assessment in clinical study using a simple temperature sensor applied directly to a subject's skin, under the guidance of infrared and/or laser speckle imaging. If validated, this technique would be comfortable, inexpensive, and unaffected by subject movement, i.e., an ideal tool for quantifying endothelial function in ambulatory and hospitalized patients. During implementation of the project in the 2011-2012 the BEPS Shared Resource designed and produced standardized reusable skin temperature sensors for use in clinical studies, developed analytical techniques, analyzed raw temperature data, performed image processing, provided designs and test results for IRB assessment of the safety of the experimental optical imaging, and assisted with data acquisition for clinical investigations at the NIH Clinical Center.